text:
What determines a plane's range?
When a planes maximum range is specified, is fuel [capacity] the only constraint or what else is taken into account?
Would it always or ever be the case that a greater fuel capacity will increase range?
Interesting long-flight story of 64 days in the air, but it doesn't get too technical: https://jalopnik.com/how-a-slot-machine-mechanic-flew-150-000-miles-over-64-5971433

As also stated in this answer:
Range is a function of MTOW and empty weight, according to the Breguet Equation for a jet:
$$R=\frac{V}{c_T} \cdot \frac{L}{D} \cdot ln\frac{W_i}{W_i-W_f}$$
with ${c_T}$ = specific fuel consumption, $W_i$ = initial weight, $W_f$ = fuel weight, $L$ = lift, $D$ = drag.
What increases range if other factors remain constant:

Higher speed $V$
Lower specific fuel consumption.
Higher lift/drag ratio.
Higher TakeOff/Landing weight ratio.

The weight ratio can be because of fuel weight used during the flight, but of course chucking ballast overboard helps as well.

The airplane's published range will be based on distance that can be flown in still air (excluding winds in other words) with full fuel, departing at max gross weight, when flown at some optimized cruise speed or mach#, at a specified flight level, with normal IFR fuel reserves (fuel to go from A to B, fly an approach, do a missed approach, proceed to alternate, fly an approach there, and land, with, for a jet, 30 minutes remaining after all that), in standard ISA atmospheric conditions.
Somewhere in the fine print in the airplane's specs will be the Mach# and altitude that the maximum range is based on.
Most airplanes can't be flown with full fuel AND a full cabin without being overweight, so you have to horse trade.  A corporate jet with fuel for 5 hours endurance may only be able to carry 3/4 of the passenger complement to get max range, or conversely be limited to 4 hours if the cabin is full.  Such a jet may have an option for a long range fuel tank add-on, increasing endurance to 6 or 7 hours, and if that tank is also full, the passenger load may be cut down to just a few passengers.

Speed, fuel capacity, and burn rate are the only three factors that determine range.  Optimizing each of these variables will lead to the most efficient results.  Generally speaking greater fuel capacity will increase range, which is why auxiliary tanks are sometimes used.
There are a great many design factors that influence each of these three variables, but that is beyond the scope of the question.  Additionally, environmental factors such as wind will affect actual performance.

Fuel capacity is fixed for a particular plane, but speed and fuel burn are not. Since drag is related to the square of speed but directly to fuel burn, flying slower can increase range.

I think we agree here...

Would it always or ever be the case that a greater fuel capacity will increase range?

The problem for a flight without external assistance is you have to carry the fuel (and any other consumables but fuel is by far the most significant consumable). You can add more tanks (and ferry pilots do), but ultimately you reach a point where your takeoff weight is at the aircrafts limits.
You could make the whole aircraft bigger, but then it needs more fuel, so you haven't really gained much.
The 64 day flight you linked was not unassisted. They received fuel and supplies from a truck on the ground during the flight. It also sounds like it was rather unsafe, with the article reporting that one of the pilots dozed off at the controls due to inadequate sleeping arrangements.


text:
What are those gray spots on the wing?
I recently flew on an Airbus A321 and noticed these gray spots on the wing, circled in red. What are those?

They are rivet ends. The paint seems to have a hard time sticking to those, not an uncommon sight on older planes.
Thanks to Darrel Hoffman's comment, I did some digging:
The phenomenon is known as rivet rash.

“Rivet rash” refers to selective loss of paint from aluminum rivet heads on in-service aircraft, as shown in Figures
1 and 2 and 3. Airlines are dissatisfied with this condition since it greatly detracts from the airplane’s decorative
paint appearance in areas most visible to the passengers, namely the 41-section (nose) and entry doors. In
addition, rivets can “rash” within six months of delivery giving the airplane a prematurely older appearance.

Quoted from Boeing Environmental Tech Notes: Rivet Rash (pdf)
A simplified explanation is that the rivets usually have a coating protecting them during storage and installation, or the properties of the rivet alloy itself may be different enough from the sheet material of the wings, that the adhesion of paint is compromized.

The real question is... what's the red circle for? Is it also common on older planes?

My guess is that the rivets cool at a different rate from the panels surrounding them, leading to uneven expansion and contraction of the paint.  You see this on ground vehicles and structures as well if they're subject to extreme cold.

@Opifex a survey of pictures of older planes in StackExchange question suggests they do indeed commonly have red circles on them.

@DarrelHoffman extremely plausible. Once a small crack in the paint forms on the perimeter of the rivet head, it's bye bye paint very quickly, considering the hostile environment they have to endure.

So it has a name, huh?  I wonder if it's called something different outside of the aeronautics industry, because I've seen it on everything from buildings to boats to park benches, etc., but the term "rivet rash" appears to be exclusive to planes.  Granted in some cases it might be nails or screws rather than rivets, but the effect is pretty much the same.

@DarrelHoffman Possibly it evolved out of "hangar rash" which is scratches, nicks and dents that result from ground handling of aircraft. Sometimes major damage caused by ground crew are also jokingly called hangar rash but they're not really (it's more in the spirits of "..'tis but a scratch"). I have heard the term "hangar rash" used around boats but it originated from people working with airplanes

@Opifex Yes, and they often have "NE PAS MARCHER" written next to them.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
define the difference between a USAF Leg vs a USAF Sortie
What is the definition of a Sortie versus a Leg according to the US Air Force?

I don't have a USAF source so can't post as an answer, but a Sortie is any individual departure on a mission of some sort.   A Leg is a segment of a flight that is part of a larger series of segments.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What's This Cable Connecting Cockpit to Vertical Stabilizer in Air Tractor AT-401?
This is a picture of an AT-401 Sprayer Airplane
I was wondering what's this steel-string stretching from cabin's windshield to the top of the vertical stabilizer
...

Possible duplicate of https://aviation.stackexchange.com/questions/24688/what-is-this-wire-going-from-mid-fuselage-to-the-tail-on-this-737

I believe it's to protect the tail from a wire strike.  I can't think of any reason someone would put an HF radio in an ag plane.

Ag operators hit small wires pretty regularly.   Cost of doing business.

Possible duplicate of What is this wire going from mid-fuselage to the tail on this 737?

@Gerry I 100% thought you were joking

It is a wire deflector. It is common for power lines to be strung at the same height that the cropduster wants to operate at, and often multiple cables at exactly the same level, so that the aircraft could be dealing with a bundle of cables as it goes forward. Power lines, especially "last runs" to individual farms or villages can be extremely hard to see from the air, often it's only the poles that are visible & sometimes they are either weathered & indistinct, or missing altogether & the wires get strung between trees. Any country road or track could have wires, & roads or tracks often mark the edge of a spraying target. Competition & economics mean the cropdusters are trying not to waste a drop of product, or miss any plants, or waste a drop of fuel/engine hours. It's one of the most dangerous aviation professions.
Cropdusters/agplanes are specifically designed for visibility of crops & the ground at low level & in steep turns, leading to the distinctive turret-like cockpit. This makes the pilot extremely vulnerable to a lethal, decapitating cheese-slicer effect if powerlines slide over the front of the aircraft. (I've also seen cropdusters that had serrated cutters on the undercarriage struts)
The deflector cable is often used in conjunction with a cutter/deflector bar mounted just in front of the pilot's windshield. You can see this bar more clearly in this photo.
http://www.airport-data.com/aircraft/photo/000001546L.html

The wire shown is a cable deflector which is part of a Wire-Strike Protection System common on most agricultural aircraft.

Wire-strike protection systems
As a last resort, when pilot situational awareness and on-board systems fail to detect a wire in sufficient time to avoid contact, a passive wirestrike protection system (WSPS) may protect the aircraft from the consequences of a wire-strike. These are designed to cut or deflect wires away from an aircraft. The types of WSPS vary depending on whether the aircraft is fixed-wing or rotary-wing. They have proven to be an effective safeguard by extensive testing and over two decades of use by both military and non-military operators' worldwide (Jackson, Boitnott, Fasanella, Jones & Lyle, 2004; RAAF, 1 997). However, to enable the WSPS to operate effectively, the wire must contact the cutter at an appropriate angle and the aircraft must also have adequate forward speed. This combination of circumstances may not always be present during low-level aerial operations.
WSPS for fixed-wing aircraft are designed to cut wires that could pass under the aircraft, in order to prevent the wires from coming into contact with the landing gear, or pass over the aircraft, possibly contacting the tail section. Serrated deflection wires may also be fitted from the cabin to the tail section, with the purpose of cutting the wire or lifting it over the tail section. Fixed-wing aircraft used in aerial agriculture operations have had WSPS fitted as standard equipment for several years.
Fixed-wing aircraft used for other purposes rarely carry WSPS as fitment often requires reinforcing parts of the aircraft and may cost several thousand dollars. In general, they are not fitted unless it is expected that the aircraft will spend many hours in low-level flight.


text:
Why would a fighter use the afterburner and air brakes at the same time?
I was looking for air brake pictures on different fighters, and then I saw a Tornado using afterburner and air brake at the same time! Air brake duty is to reduce speed, isn't it? So why would a fighter burn so much fuel to increase thrust and then use speed brakes simultaneously?

While the pictures above are most likely a result of the reason posited by ymb1 (showing off max blast while staying subsonic for the crowd), using afterburner with speedbrakes to reduce weight is a known practice in the fighter community, in line with Kolom's answer.  Even if an aircraft is equipped with a fuel dump system, environmental restrictions and standard operating procedures limit the altitude at which fuel may be dumped; if already below that floor, using afterburner with speedbrakes extended is a practical way to reduce landing weight. I don't have any specific sources to cite, just drawing on my experience as a naval aviator.

In KSP I've had to use brakes as control surfaces when things go wrong. Is there any possibility this is poor man's thrust vectoring? Say, if you wanted to do a back-flip into a stall on a dime.

@Mazura: I'd guess that's unlikely; fighters have large control surfaces that give plenty of control authority even at low speed.  Possibly if your elevators are damaged, and the speed brakes aren't at the centre of gravity or lift...  If you wanted to perform a cobra maneuver you'd maybe have afterburners on (for thrust to hold up the plane's weight) and speed brakes on (for the speed-limiting effect, not extra control authority).  But according to Wiki, you normally apply thrust part way through.


text:
Why do they tell you to tie your lifevest on the left side during safety briefings?
This might be UK specific, given I have only been flying internally recently.
During the safety briefings, when describing how to inflate the lifevest the instructions are always:
"Wrap the lines around you and tie them using a double knot on your lefthand side".
I have asked the crew and none of them can tell me why and I cannot find any reason online there is an emphasis on the lefthand side.

Is the lines of such length that it's possible to do it on both sides? Maybe it's like the offset length headphones you have behind your head? I have never had one of those vests on so it's just a guess.

From what I can see, the lines are the same length.

Right side means you are in a relationship (or don’t search a partner/chat up), left side means your free and not in a relationship. Backside - widow - or just for practical reasons, during working or when the lines are just to short.

Maybe it doesn't matter if tied left or right but they just tell it so that people don't start asking when the emergency comes.  Also, if all people tie it on the same side, the tying doesn't interfere with your neighbour's tying because of the limited space in a passenger's seat. It may also be easier for the FAs to check the knots if they can be expected in a defined place.

After many questions to the various crew members/ground crew on the next few flights I did, I have managed to get an answer that makes sense.
You are told to tie the life vest on the left side for two reasons:

The inflate toggle hangs on the right side of the lifevest and if you were trying to tie the knot below it then you might pull it by accident, inflating the lifevest inside the plane.
If you tie the knot with a bow, instead of the double knot, then if the bow was on the right side there is a chance that you will get it tangled in the pull toggle while moving around the plane, inflating it before you exit.


text:
Is "margin final" an ATC instruction in USA?
I was south-east of the airport and the active runway was 24. The ATC said, "Make straight in and remain south." And then he said, "Margin final, cleared [to] land."
What is margin final? I'm an international student so I may have misheard. I thought it's for joining final so I said, "Join final, cleared to land." The controller did not say anything after.
If it wasn't "margin final," what could it have been?

The literal answer to your question is no: the word "margin" isn't used that way in either the ATC orders or the PC/G. But if you want to know what the controller actually said, can you tell us which airport it was, the day and time you were there and your tail number? Someone may be able to find it on liveatc.net.

What about 'merge on the final'?


text:
Question about federal airways in Class E airspace going from 5500 MSL(USA)
Class E with a floor of 1,200 feet AGL is shown with the "fuzzy" side of the blue. And sometimes Class E has a floor higher than 1,200 feet. They will print the floor of the Class E altitude in the "fuzzy" side of the blue. I know the Class E with a floor of 1,200 feet AGL is usually the floor of an airway. It goes from 1,200 AGL to 18,000 MSL. But if there is a designated specific altitude higher than 1,200 AGL for Class E airspace floor covering a federal airway, at what altitude does the Federal Airway start?

Likely at the floor of the Class E airspace.  A Federal Airway coinciding with a Class E floor higher than 1200' AGL would normally only exist in mountainous terrain.
A definitive example could be found by looking in the FAA's "Airspace Designations And Reporting Points" document, available on-line.


text:
What does it mean to move a single flight control to its full deflection?

It is the speed below which you can move a single flight control one time, to its full deflection, for one axis of airplane rotation only

This is part of the explanation of maneuvering speed.
What does 'full deflection' mean?
Is applying full rudder full deflection?
Is turning the yoke 90 degrees full deflection?
What about in the pitch axis?

Yes, that is correct. Moving any control surface until you hit the stops is considered "full deflection". For the purpose of maneuvering speed, this is the speed at which any single control surface can be fully deflected without risking damage to the control surface or structure.
Pitch is full back/forward on the yoke or stick, which is where the elevator stops movement. This isn't always 90 degrees for ailerons, especially in aircraft that have stick controls versus yokes.

The maneuvering speed is the maximum calibrated airspeed at which - starting from straight and level flight - you can safely move any single flight control from the neutral position to the maximum deflection possible at that airspeed.
What constitutes full deflection varies from aircraft to aircraft, and also - frequently - with airspeed.  At low speeds, it is generally limited by the control surface's mechanical stops (those thingies which physically block the control surface in question from moving to a greater deflection); at higher airspeeds, depending on the aircraft, it can be limited by an additional, moveable mechanical stop (which limits the control surface to a smaller and smaller range of deflection as airspeed increases), by the amount of force available with which to move the control surface (in which case, at high speed, the control surface's actuators are physically incapable of deflecting the surface past a certain amount, and the possible range of motion decreases as airspeed increases), or, in some cases, by the mechanical stops for the yoke, joystick, or rudder pedal (for aircraft in which control-surface deflection at high airspeeds is limited by a mechanical ratio adjuster, such that, say, turning the yoke all the way to its stops commands less and less aileron travel as you go faster and faster).
The maximum speed at which a full-scale deflection in the pitch axis is safe is frequently different from the maximum speed at which a full-scale deflection in the roll axis is safe, which is, in turn, usually different from the maximum safe speed for a full-scale yaw input.  The maneuvering speed of the aircraft as a whole is the lowest of these speeds (which is generally the limiting speed for the pitch axis).
Note that being at or below maneuvering speed only guarantees that a structural failure will not occur if, starting from straight and level flight in an undamaged aircraft with all control surfaces originally in their neutral positions, one single control surface is deflected to its limit.  If you start out in an aircraft weakened by undetected fatigue damage, or if you push two or more control surfaces in different axes to full deflection simultaneously, or if you take a control surface from full deflection in one direction to full deflection in the other (especially if done multiple times in a row) rather than merely from the neutral position to full deflection in one direction, continued airframe structural integrity is not guaranteed.  To quote Wikipedia:

It has been widely misunderstood that flight below maneuvering speed will provide total protection from structural failure. In response to the destruction of American Airlines Flight 587, a CFR Final Rule was issued clarifying that "flying at or below the design maneuvering speed does not allow a pilot to make multiple large control inputs in one airplane axis or single full control inputs in more than one airplane axis at a time". Such actions "may result in structural failures at any speed, including below the maneuvering speed."[3]

Anonymous downvoter, show thy face and explain thy action.


text:
What does 'smell smoke' mean?
As to private pilot course, I learned emergency procedure of engine fire. In POH, there is engine fire procedure and electrical fire procedure. When examiner or other chief instructor say 'I smell smoke', what does it mean? Does it mean engine fire?

What does it mean?

Generally it means something is on fire (or burning)

Does it mean engine fire?

It might, but there are lots of things in an aircraft that can burn so it might not always be an engine fire. Electrical fires can produce strong smells as can burning insulation or other non engine related fires.
As per the comments, the key is to work through your checklist items to determine the source of the fire and mitigate appropriately. For example here is a snip of the fire checklist for the PA-28-161 I trained in:

Its important to note that electrical fire is the first item on this list, when trouble shooting you dont want to shut off a running engine to discover its an electrical fire.

So, just saying 'I smell smoke' is kind of vague order on checkride, right? I'm confusing that when an examiner say like that, it mean fire engine or electrical fire.

@gusdyd88: The examiner is not telling you where the fire is because s/he wants you to go through the appropriate procedures for a suspected fire, discovering if it's the engine, electrical, or your passenger in the back seat sneaking a cigarette.

@jamesqf Then, it depends on my choice. When examiner say 'smell smoke', I can pretend there is engine fire, electrical fire or smoking passenger. According to the situation I choose, I can proceed appropriate procedure.

Play along, ask your instructor "does it smell like electrical smoke?  Do you see smoke coming from the engine cowling?  Is there visible smoke coming from behind the radio panel?"  You won't discern his intent for the simulated emergency by asking the internet.

@gusdyd88 if you're not how your instructor expects you to react during a training exercise, you can just ask, and even role-play it on the ground. He probably does it so often that he assumes everyone is familiar with the technique, and may have not realised that he's not done anything similar with you yet.


text:
what is the actual infrastructure of the current US NOTAM system?
After a Jan 11 2023 NOTAM outage, FAA and news outlets have reported there was a "damaged database file" and a problem with the backup. A government contractor, Spatial Front, was connected with the outage, and more detail was given:

after contracting personnel “unintentionally deleted files” while working to correct synchronization between a live primary database and a backup database for the IT system.

There's been a lot of public discussion explaining what the NOTAM system is and why it's important, but I haven't been able to find technical details on the database and system. Not just "a database file".
For instance, it might be PICK/Basic on Solaris, or DB2 via Cobol on z/OS, or MS Access on Windows NT 3.51. That's the level of detail I'm curious about.

(would this be a better fit on stackoverflow? I came here because of the domain specific knowledge)

I think this site is better. SO is for questions about programming, while this question is about how a database related to aviation is configured.

I've not seen a detailed breakdown on how the NOTAM system works, but we do know three things
NOTAMs are issued from a database

The FAA said preliminary indications “traced the outage to a damaged database file.”

This system is really old

When the Transportation Department made its annual budget request to Congress last year for the FAA, it sought $29.4 million to accelerate development of a program that would let the agency eliminate what it called “failing vintage hardware” that currently supports the Notam alert system. The system has failed at least two other times since early 2021, industry officials said, though in those cases the FAA was able to avoid widespread impacts to flights.

Possibly 30 years old

The Federal Aviation Administration software that failed Wednesday causing thousands of flight delays and cancellations is 30 years old and at least six years away from being updated, a government source familiar with the situation tells CNN.

An employee replaced files, causing the outage

The issue apparently occurred during routine scheduled systems maintenance, a senior official briefed on the internal review told ABC News. An engineer "replaced one file with another," the official said, not realizing the mistake was being made. As the NOTAM system began showing problems and ultimately failed, FAA staff feverishly tried to figure out what had gone wrong. Engineers and IT teams are now working to keep the system from crashing again, while also trying to figure out if there are any similar systems that could fail without redundancies.

What are they using?
The odd part is the mention of "replacing files". Now, a failed drive can cause all sorts of issues (sooner or later you have to write data to disk), but generally you don't do relational database maintenance by "replacing files". What this suggests is that they are not using a relational database at all, but an older system known as a flat file database

A flat-file database is a database stored in a file called a flat file. Records follow a uniform format, and there are no structures for indexing or recognizing relationships between records. The file is simple. A flat file can be a plain text file (e.g. csv, txt or tsv), or a binary file. Relationships can be inferred from the data in the database, but the database format itself does not make those relationships explicit.

In other words, these files are essentially stripped-down spreadsheets (i.e. comma or tab separated columns). This would better mesh with the statement about "failing vintage hardware". If this system is really old, it may be running on something written in an older language like pure COBOL or ADA. In a flat file system, you would be fiddling with files, and any errors in the file could mess the whole system up. This would also mesh well with a system in use since the early 1990s, when RDBMS systems were not yet as widely used as they are today.
This article from 2008 contains this

The system itself is called NADIN (National Aerospace Data Interchange Network). It was designed by North American Philips for the FAA in the early 1980s. The two Philips DS714/81 mainframes became operational in January 1988. The company went out of business later that year, and the FAA bought out the entire parts inventory.

1988 would put this around 35 years old. This article has this  note

Isaksen uses two Philips DS714 mainframe computers as his message-switching network. The DS714 was originally manufactured in 1968 and upgraded with new processors in 1981. Since then, they have been getting increasingly harder to maintain, support and write code for.
"These machines don't really have an operating system," says Isaksen. "This was in the days when the assembly language was written directly to the machine. We have hardware that is no longer supportable."

This system was running the FAA traffic system, but this blog suggests it might have also been running NOTAM

According to this story, the system launched in 1988 on a pair of Philips DS714 mainframe computers. Philips quit the computer business shortly after these machines were installed. This article from 2005 talks about the FAA’s plan to replace the Philips mainframes and to “go online early next year [2006]”, but apparently they haven’t completed the porting project. The volume of traffic is larger than you’d expect, with 1.5 million messages per day (about 20 per second; roughly what a pizza-box Web server might be expected to handle), apparently because the network handles weather and NOTAM data as well as flight plan data.

This would reinforce my suspicions that it's a giant flat file system, since such a machine would be unlikely to run Oracle, and highly unlikely to run IBM's DB2 (which IBM sold hardware for).


text:
Do most aircraft require a nose-up attitude for level flight?
I recently saw a picture of a HUD on a commercial plane, and I noticed the nose was level to the horizon but the flight path indicator is almost always under the horizon line no matter the speed, does this mean most commercial jets require a slight nose-up attitude to fly at a level and consistent altitude?
https://c8.alamy.com/comp/PJJCKW/aircraft-heads-up-display-hud-on-a-modern-boeing-787-airliner-PJJCKW.jpg
Similar to that


text:
What does the lift coefficient take into consideration for flaps?
Angle of attack increases lift for two reasons, Camber and increased flow deflection, What reason does the lift coefficient use? Both?

The lift equation is:
$$ L = C_L \frac{\rho \times v^2}{2} A , $$
where $C_L$ is the lift coefficient, $\rho$ the density of the air, $v$ the relative velocity and $A$ the wing area. The idea behind the lift coefficient is to combine all aerodynamic effects related to the shape of the aircraft into one dimensionless number, which can be experimentally derived as a function of the angle of attack:

(example lift curve from Wikimedia)
When extending the flaps, two things can happen:

The shape of the wing changes, i.e. wing camber is increased. This will modify the lift curve:

(image taken from this answer)
The total area may increase (e.g. for Fowler flaps, see also this question: Does deploying flap change the aspect ratio of the wing?).

So the $C_L$ is taking the change in camber into account, but not the change in area, which will also contribute to increased lift.


text:
How does speed affect lift?

I understand the lift coefficient shown above. But does lift increase with speed, and how?
I understand I can't apply this to the graph as it is a coefficient, but if I had an angle of attack of 10 degrees and a speed of 0 knots, we would obviously have no lift assuming there isn't any wind, but if we increased our thrust and speed, we would gain more lift, and if we increase AOA even more, we get even more lift and the same with thrust.
But what about 0 degrees with symmetrical airfoils, does lift also increase with speed, and does it work similar?

Note that if you want no vertical acceleration (constant V/S, zero is also a constant), your lift must remain the same (Newton explain that better than me). Thus if you change your speed, you must change AoA to keep the same lift.

The lift equation is $$L = \frac{1}{2} C_L · v^2 · S · \rho$$
where $S$ is wing area, $C_L$ coefficient of lift, $\rho$ air density, and $v$ airspeed. Using units of measure $\text{m}^2$ for $S$, $\text{m}/\text{s}$ for $\text{v}$, and $\text{kg}/\text{m}^3$ for $\rho$, the result is lift in $\text{N}$ (newtons).
Concerning symmetrical airfoils, they work quite well too, and the equation given above is perfectly valid for them. If it’s true that at zero degrees their $C_L$ is zero, they give zero lift regardless of the speed (zero times anything is zero).

so if we were to increase angle of attack, that increases the lift, and increasing the angle of atack and increasing the power, increases the lift even more, and if we wer e at zero angle of attack, we still get lift from an asymmetrical airfoil that too increases with speed?

@JamesDavis Changing the AoA changes the CL (Lift coefficient).  For an AoA where CL is not zero, the total lift will be proportional to the square of the velocity.  In your example chart CL goes to zero at an AoA of -5 degrees.  If you maintained an AoA of -5 degrees, then, the wings would generate no lift, regardless of airspeed.  Anything above that AoA will generate lift proportional to the square of the velocity.

The lift equation is idealized. The coefficient of lift versus angle of attack curve changes as speed and/or wing chord change. This is why air foil calculators like XFOIL also need Reynolds number, in addition to the air foil information to generate polars (lift vs aoa, drag vs aoa). Beyond some critical speed, due to flow separation, CL versus AOA decreases.

If you have a fixed aerofoil in a wind tunnel, lift increases with the square of the air speed.
However a real aircraft usually only needs enough lift to balance its weight, so as it flies faster it will also decrease the angle of attack to keep the lift constant.
Conversely, if a pilot wants more lift in order to make a tight turn, he will usually increase the angle of attack rather than increase speed.
Lift also increases with air density and wing area (as per xxavier's answer), but those are usually outside the control of the pilot!

It's difficult (impossible, really) to predict what happens based solely on air speed.
To get a meaningful result, you need to go by Reynolds number. Normally, you'll have a completely separate graph for each tested Reynolds number. At a different Reynolds number, not only with the lift change, but the basic shape of the Cl/alpha line is likely to change (e.g., as the Reynolds number drops, it's pretty routine to get a much "sharper" stall--that is, where your graph shows a nice, smooth roll off in lift as the AoA increases, at a lower Reynolds number, it might easily have only minimal loss of lift, then drop much more quickly. For example, here's a Cl/AoA graph for a NACA 6409 airfoil:

The gold line is at Re=1,000,000, the teal at Re=50,000. These are both quite low, but at least give the general idea. Note in particular that the curves have substantially different shapes. At Re=1M, the lift increases almost linearly with AoA, right up until it approaches stall (at which point it rolls off quite smoothly). At Re=50K, the increase is much less linear, and Cl increases sharply shortly before stall, then drops like a rock, with almost no warning at all.
But also note that it's all about Reynolds number. Low air speed with a large chord acts much the same as a much higher air speed with a much smaller chord.
For a concrete example, the airfoils used in the impellers of a jet engine operate at high air speeds, but have extremely small chords. This gives a very low Reynolds number despite the high air speed. Even for a supersonic jet, the impellers are often operating at a lower Reynolds number than the main wing of something like a Piper Cub or a Cessna 172.

At Reynolds numbers > $10^7$, at fully turbulent flow, the lift curves would be pretty close though. In fact so close, that the idealised lift equation of @xxavier’s answer can be used for practical computation of lift.

Welcome to Aviation Stack Exchange James! A simplified answer would be:
Lift is produced by airflow around the wing (expression for this is given in xxavier's answer). If you increase the speed, you will increase the airflow around the wing. Given everything else stays constant, you will get more lift. (IRL the consequences of increased speed and lift are numerous, but beyond the scope of this question)
For a symmetric airfoil at zero AoA the Cl would be 0, and speed would have no effect on lift: regardless of speed, lift would be zero.


text:
Why do light aircraft stall their wings to land?
What's the advantage compared to large commercial aircraft that don't stall their wings on landing?

This is a question based on a false premise - the vast majority of planes do not stall to land

Just because the stall warning horn is going off, doesn't mean the aircraft is stalled.

My apologies, I was told the technique for light aircraft such as cessnas was to stall the wings at the moment of touchdown, and the horn sounds at the moment of stall, my apologies, I'm assuming it sounds to the lead-up of a stall.

Light aircraft DO NOT “stall their wings in order to land”. To allow this question to remain open will only add credence  to this incorrect misconception.

@MikeSowsun Not sure why you think that it is a misconception. A great landing has minimum forward and vertical speed and the way to accomplish that is to be just at stall speed when you touch down. If you do your roundout right, the wings stall just as the wheels touch down. It’s easier to do on a low wing airplane than a high wing, but either way, that’s the goal.

Go out and practice stalls. Note the IAS and nose up attitude in degrees. Now go practice your landings and compare. The vast majority of aircraft are not stalled when they land. It is almost not possible as most tricycle gear aircraft would strike the tail and most tail draggers would touch the tail wheel and then cause the nose to lower before the stall actually happened.

What makes you think small aircraft stall to land? You may elaborate this point by giving examples so that the answers can be more specific (I suspect this is done for a really small number of aircrafts and examples can show what types of aircrafts are concerned)

Does this answer your question? Is it okay to purposely stall a small single-engine aircraft just before touch down to get a good flare?

A full stall landing is generally a bad idea for everyday flying, regardless whether you're in a Piper Tomahawk or a 747.  The slightest error can lead to stalling well above the runway surface, resulting in a drop that can injure the pilot and passengers, damage landing gear, and in some cases even damage the fuselage structure or main wing spar.  Even if perfectly executed, it also leaves you in a very bad position if, for some reason, you need to go around -- you've given away all your energy and have to get enough of it back to not only keep flying, but climb, and do it before you run out of runway or obstacle clearance.
A full stall landing is a special STOL technique, and most pilots require intentional retraining to do it, because the approach is flown much more slowly than normal -- normal approach speed, what pilots are trained to do routinely, has a significant margin above stall for safety (because a stall at low altitude, even in absence of a spin, is likely to result in a potentially fatal crash).
Even a "three-point" landing in a conventional gear aircraft isn't usually flown as a full stall -- the airplane can assume the three-point attitude and still be below stall AoA, assuming the descent angle isn't too steep.

Then why does the stall horn sound before landing in cessnas?

The stall warning in most airplanes that have it is based solely on angle of attack, and is set up to sound several degrees before actual stall occurs.  The stall horn in a Cessna 152 will sound during flare after a minimum speed approach, but that means you're approaching stall condition, not that you're stalled.

When I started training (the rules have since changed), slow flight was to be done with the stall warning activated but without actually stalling. Do that for a while and you discover there's a fairly large margin between them.

@James Davis:  A stall warning (it's a light in my Cherokee, not a horn) wouldn't be much use if it didn't activate until you actually had stalled.  With a little practice (should be part of basic training), you can fly as long as you want right on the edge of stall, with the warning going off, and that's slower than I would actually land, even on a really short field.

When you land you want to be as slow as possible to minimize ground roll, maintain control, and reduce stress on the landing gear. Ideally, you will stall the airplane a few inches above the ground. If you stall the airplane a few feet above the ground you will “drop in” and have a hard landing. Ask me how I know.
If you are much above stalling speed you have more energy to dissipate on the landing roll. This could be a problem if there is a strong crosswind or a short runway. One of the things the FAA stresses is to always fly a stabilized approach and landing—even if you don’t need to for a particular runway. You may not need the precision on a 6,000' long 150' wide runway but it comes in handy when you land at a 2,500' long 50' wide grass strip.
As the FAA explains in the Airplane Flying Handbook:

Touchdown
The touchdown is the gentle settling of the airplane onto the landing surface. The round out and touchdown are normally
made with the engine idling and the airplane at minimum controllable
airspeed so that the airplane touches down on the main gear at
approximately stalling speed. As the airplane settles, the proper
landing attitude is attained by application of whatever back-elevator
pressure is necessary.

Edit:
Wolfgang Langewiesche and others disagree with Zeiss Ikon. Talking about taildraggers, “The exact length of the landing gear legs depends therefore on just how much the designer expects the pilot to slow the ship up before setting it down. In most airplanes, the designer goes pretty near the limit in this respect; he expects the pilot to slow the ship up to actual stalling speed before letting it touch the ground, and he proportions his landing gear accordingly.”
Michael Love in his book Better Takeoffs and Landings, writes about tailwheel three-point landings. “In the textbook full-stall landing, the airplane touches down on the main gear and the tailwheel at the same time. The airplane should be fully stalled as it touches down…”
He writes that “Tricycle-gear aircraft should be landed in a nose-high position, touching down on the main landing gear, with the nosegear off the ground. Figure 4-6 shows a typical tricycle-gear airplane correctly executing a full-stall landing.…The aircraft is approaching a full-stall just as it touches down.”
I have taken instruction from instructors certified by the Bonanza Society under the Beechcraft Pilot Proficiency Program. They teach that you should aim for full-stall, full-flaps landings every time.

Touching down at "approximately stall speed" isn't at all the same as "stall the airplane a few inches above the ground."  Minimum control speed is above stall speed for many aircraft, also -- and you need to have good roll, pitch, and yaw control available during flare and touchdown, especially if there is any crosswind at all.

It might be a good idea for "designers" to actively communicate with pilots and to utililize their experience as a database for improvements.


text:
Is there a V speed for the point an aircraft starts an ascent at 0 angle of attack?
Some aircraft with an angle of incidence or cambered airfoils are capable of climb without any angle of attack, Is there a V speed for the speed at which an aircraft starts a positive climb?

I'd like to point out that aircraft with an angle of incidence does not equate to zero angle of attack.  It means that the wing will have a positive angle of attack when the fuselage is aligned with the relative wind.  Regarding your question:  I will let the engineers answer, but yes, if a wing is capable of producing lift at zero angle of attack it will obviously start climbing once it attains a certain speed...  Are you asking how to calculate this?

No, there is no V-Speed associated with zero angle of attack, nor is climb associated with angle of attack. Since zero angle of attack does not directly translate to minimum drag for a production aircraft in operation, it is not a meaningful performance gate, which is what V-Speeds are designed to represent.
However, this is not to say that having a zero flow incidence against the fuselage is not desirable:

If the body-axis is aligned with the fuselage longitudinal axis, it would be desirable from a passenger comfort standpoint to fly at zero AOA during level cruise. We don't want to have an inclined martini glass for the whole duration of the flight.
Non-zero flow incidence against the fuselage does create drag. It would be desirable from a performance perspective to decrease any form of drag during cruise or climb.

This is achieved during aircraft design. The wing setting angle against the fuselage is tuned such that the average operational flow incidence angle against the fuselage is minimized.

My apologies, I'm confused, My question was for if there was a V-Speed Indicating the aircraft speed at where the lift force would be equal to weight at a zero angle of attack, such as a "Level flight" speed. (Of course, very dependent on the current weight of the aircraft such as fuel level and passengers aboard)

"Vtos" Is the minimum speed for climb with one engine operative, But what about in normal function? I was thinking vlof, but that does depend on angle of attack due to rotation on takeoff.

@James The question is, why do you want to lift off at zero AOA? What's special about zero AOA? If you have a tricycle, being able to rotate allows you to decrease the drag during ground roll, which increases field performance.

general aviation question for me honestly, What about a cruise/level flight where you want to be as level as possible without a change in pitch? ( I understand on my airplanes this requires a 1-2 degree nose up attitude )


text:
How much lift do supercritical airfoils produce?
Compared to your regular asymmetric cambered airfoil, How much does lift do supercritical airfoils produce?

Supercritical aerofoils and 'regular' aerofoils have characteristics that suit them to different applications. The lift produced depends on airspeed, angle of attack and other factors. You can't say that a supercritical aerofoil produces n times the lift of a regular aerofoil without being specific about the conditions.

Supercritical airfoils produce comparably more lift than conventional cambered airfoils but less than optimised high-lift airfoils. This is because

they have blunter noses which work over a wider angle of attack range,
the blunt nose also allows to use effective slats or Krüger flaps,
they have plenty of camber in the aft section of the airfoil and
the high rear loading allows for thin, highly cambered flaps.

From history.nasa.gov:

In the course of developing the wings for these flight programs, it was learned that the supercritical airfoils had excellent high lift characteristics because of their large leading-edge radii. This important benefit tended to offset the fact that their subcritical profile drag is higher than for comparable 6-series sections.

However, the forward part contributes relatively little to lift because it has negative camber. Also, the rear loading causes a high pitching moment.
In the supercritical speed region their upper side produces more suction since local speeds can reach up to Mach 1.3 while conventional airfoils must struggle to keep speeds subsonic. Part of that advantage is used up by making the airfoil thicker so suction on the lower side is also higher than on conventional airfoils, but an advantage remains. More recent airfoils add some more lift at the nose by designing a slow speed rise on the lower side while the upper side accelerates the local flow more quickly. Their main lift, however, comes from the thin, highly cambered aft section.
When R. Whitcomb researched supercritical airfoils, he noticed their high subsonic lift and modified the general shape by adding more forward camber into the GA(W)-1 and -2 (General Aviation Whitcomb) airfoils which became popular choices for modern GA aircraft due to their high lift and benign stall characteristics (witness 93 hits on Dave Lednicer's incomplete guide to airfoil usage, among them the Piper PA-38, the Glasair and the Edgley Optica).

@RobertDiGiovanni Modern super-critical airfoil can be thin and have large stall AOA (at least in non-icing, contamination-free condition).

Peter Kampf, appreciate your continued refinements.  Perhaps the question would be better phrased as "which wing produces more lift at a given speed" as this has become an incredibly relevant subject for newer airliner wings and could lead to improved procedures for when to apply slats and flaps.

The larger leading edge seems to universally improve higher AOA characteristics, particularly Clift/Cdrag vs Alpha, where many of the sharper leading edge designs begin to fall off at around 5 degrees!  Looking at even some of the early Gottingen thick airfoils, amazing that their lift to drag was very favorable (So to save drag use a smaller Gottingen).

"...while conventional airfoils must struggle to keep speeds subsonic" Must they? They should, primarily for the sake of lower drag, but strictly speaking the OP didn't ask about drag ;) Given the same conditions (which we must assume for fair comparison), local speeds (or rather, peaks) will be higher on the conventional airfoil, and the question is (indirectly) how that will affect lift. I don't think it's clear from the paragraph; some may even conclude that speeds are lower...

@Zeus this is why the Reynolds number formula may need a Mach factor built in.  At lower Mach, "conventional" airfoils benefit from accelerated airflow (circulation) over the top, but, as aircraft speeds increased, began to encounter the shockwave "barrier".  Without taking Mach into account, at lower airspeeds, "supercritical" lift to drag performance (especially while maneuvering and actively changing AOA) is rather poor, particularly with sharper leading edges.  I am hoping this leads to better "when do we fully retract slats and flaps" SOPs.


text:
Why/How does the Pilatus PC6 Approach nose-down?

How is it possible, and why?
Why is the aircraft not overspeeding?
I understand it has beta thrust, so would that be an explanation? What are the advantages to such a steep approach?

How: With flaps out and the engine at idle that is the pitch for this aircraft that will yield its maximum decent speed.
Why: Max rate decent are commonly trained to be used in emergency situations but in this case its likely being used to save time since jump planes make money jumping. In most situations passenger comfort and airspace organization limits decent rates and keeps them controlled. Jump planes simply serve the purpose of getting passengers to jumping altitude and then getting back on the ground to scoop up the next load so max decent is used to save time.

Is the engine just idle or in beta?


text:
What is stall speed exactly?
I used to simply think It was the speed where any attempt to pitch up to maintain an equilibrium between lift and weight would result in flow separation, But Wikipedia says;
But I noticed in a Sim I play, The stall buzzer plays whenever the airspeed gets under a certain point, No matter what angle of attack?
I first thought this was a bug or flaw in my simulator, But why on earth would there be a stall? As said before, stalling is not dependent on speed, so what exactly is "Stall speed"?

That doesn't seem right. Does your sim show you what the aircraft AOA is?

Stall speed is whatever airspeed you have when the wing reaches the stall angle-of-attack.  When we say  "stall speed", we often mean the 1-G stall speed, but under the right conditions we can place the wing at the stall angle-of-attack at a higher or lower airspeed.
The simulator may have a flaw.  Also, you may not have a good understanding of what angle-of-attack is, and how it relates to pitch attitude.  What exactly makes you think that the wing is not near the stall angle-of-attack whenever the stall buzzer is on?  Just because the nose is below the horizon?  That would be a misconception.  In  a high-drag, low-thrust descent, the flight path can be so steep that the nose can still be below the horizon even when the angle-of-attack is quite high.
In straight-line (unaccelerated) flight, angle-of-attack is much more closely related to airspeed than to climb rate or sink rate.  In wings-level straight-line flight, for shallow to moderate climb or descent angles, the relationship between angle-of-attack and airspeed has essentially nothing to do with whether the aircraft is climbing, descending, or flying level.  In these parts of the flight envelope, to a first approximation, any given airspeed is associated with with one particular angle-of-attack, regardless of the climb rate, sink rate, or pitch attitude.  It sounds like this is what you are seeing on the simulator.  This is normal!
Your question suggests that you may think that a descending flight path is evidence that the wing is producing less lift than in level flight, and therefore should be harder to stall, or should stall at a lower airspeed.  Actually, inadequate lift is not the fundamental cause of a descent, and for shallow to moderate descent angles, the wing is only creating very slightly less lift than it would in level flight, creating an imperceptible change in the unaccelerated stall speed.
To check the functioning of the simulator, try pitching up into a very steep climb that forces the airspeed to decrease.  When the stall buzzer comes on, can you make it go off immediately with a very aggressive forward push on the stick or yoke?  If not, something is probably wrong with the simulator.
If everything is working right, with some practise, you should be able to fly a semi-ballistic arc with the G-load near zero as you go over the top, and with the airspeed dropping well below the normal stall speed as you go over the top, without the stall warning buzzer coming on.  This will be easier to investigate if the simulator includes a G-meter.
If some parts of this answer don't make sense to you and you want to better understand the balance of forces in level, climbing, and descending flight, some of the links given at the end of this answer may help: How does an aircraft descend without its nose pointing down?
For more, see the "See How It Flies" website, especially chapter 2.

Surely there are answers somewhere on ASE that illustrate how an aircraft can stall even with the nose below the horizon-- links to those answers should be added to this answer.

The aircraft I was using Was pitched down heavily with airbrakes, But Hey, Only so much in FSX

Sounds normal; see expanded answer

@JamesDavis, for greater details, see also How It Flies, especially the chapter 2.

Great resource, could be added to answer.

Future edit: this sentence could be reworked a bit.   It is not true at extremely steep climb/ dive angles.  I.e. near vertical.  "In straight-line (unaccelerated) flight, angle-of-attack is much more closely related to airspeed than to climb rate or sink rate."  The next sentence clarifies the situation better.  Also, need to add the actual links to the See How It Flies reference.   Also, would be good to ask if sim has an AoA gauge, and if not, suggest finding one that does.

future edit: "creating only an imperceptible change"...


text:
How is the glideslope intercepted on final approach?
On ILS, If you're low you pitch down and reduce power, and if you're high you pitch up and add power.
I'm assuming it works like this;
--- If you pitch up without adding power, You will intercept the glideslope but slow down too.
--- If you power up without pitching up, You will intercept the glideslope, But speed up too.
--- If you power up and pitch up, You will get extra lift by the extra speed, Then bleed off that speed by pitching up, But replacing the lift from the speed with the lift from the angle of attack?
EDIT: Also when pitching down and reducing power to intercept a glideslope, You're technically losing allot of lift? So is that done by simply not reducing lift under power, But instead kinda "nosediving" and directing its speed slightly downwards?

If you're high & you pitch up and add power, that isn't a correction - it's a climb. Please rewrite your question to say what you mean.

<On ILS, If you're low you pitch down and reduce power, and if you're high you pitch up and add power.> that's a good way to avoid the glideslope, not to intercept it.

You may read how it flies. This website is full of resources that may help you understand how to keep track in all dimensions (among other things).

It looks like your first sentence may not really say what you meant to say.

Did you mean to say:  "if the glideslope bar on the display is high you pitch up and add power"?  Because that will be the indication you will see if you are low.  (you have things backwards...)

I think you are overthinking this.
You adjust speed by changing pitch (moving the stick forward or backward). You adjust descent rate by changing the throttle.
When intercepting the glideslope, you reduce throttle to start descending. Adjust pitch to keep the correct approach speed, and adjust throttle to stay on glideslope.
In terms of controlling the plane, flying an ILS is no different from flying any other kind of approach.

This is the technique taught to carrier pilots by the United States Navy. Control the AOA indexers with the right hand on the stick, and the GS or "meatball" with the left power hand. Of course inputs need to be coordinated together as others have pointed out, but in general you will lead the correction with one or the other input, adjusting the other as necessary.  This basic method translates well to flying ILS approaches.

The only downside to this is that the A/C is sluggish and does not respond as fast to pilot inputs as a pitch/power correction for glideslope and power for airspeed.

Maybe what you fly is sluggish!  :)  But who am I to talk, anymore at least... Has-been that I am.

You’ll get multiple answers on this, but my personal preference as a certified flight instructor is that on final, one should use pitch and power inputs to adjust for glideslope deviations and power inputs to adjust for airspeed deviations.  This is the method taught to pilots by the United States Navy, and it works very very well for flying extremely precise approaches.

Where did you hear that?  Pitch and power are obviously inextricably linked, but the fundamentals we taught USN carrier pilots are the same as in the real world: Pitch controls airspeed/AOA, and power controls glideslope. Understanding and managing your energy state is key.  I personally use both as you do, but I'm downvoting for the erroneous attribution of your technique to the USN.

Actually, that's how an autopilot flies it no?  The AP pitches to glideslope and you control speed yourself with thrust/power.   The AP takes care of trim issues itself, but for hand flying, the critical item is trim and getting good at trimming to the approach condition so continuous pressures aren't required.  The glideslope is a unique case where the normal rules of pitch to speed are ignored in order to maintain a precise glide path line.

@John K - Correct in how the AP flies an ILS.  And autothrottles would control speed on a fully coupled approach.  However, not sure what you mean by "normal rules of pitch to speed are ignored"...

It's a reference to the basic rule that pitch and trim ultimately controls speed, and power/thrust ultimately controls climb/descent.  If you are flying along and sinking, say descending below an altitude, you might just add some power and wait for the airplane to climb to the altitude you want on its own time.  On a glide slope this takes too long because you are shooting for a very precise path, so you just pitch to path and follow up with power and trim.  In other words, pitch is the priority tool to maintain the flight path on an ILS.

I learned that technique from a naval aviator who used it his day job to snag three wires aboard ships in an F-18.   People often teach pitch for airspeed power for altitude for final approach. However this technique is better suited to constant airspeed climbs or descents and has quite a few limits to it and usually results in an inaccurate approach. Pitch in power for glideslope power for airspeed is a much better approach and final.

@John K - I am not disagreeing with your points, but pitch first for glidepath is overly simplistic.  If you are low and slow you'd better lead with power first!

@Carlo Felicione - Hornet guys are notorious for picking up bad habits from using the HUD. They also have really good autothrottles that they use more frequently than others in the airwing, so they do get used to controlling glideslope with pitch.  I don't know what your friend's experience level and credentials were, but I was a Fleet Replacement Squadron qualified Landing Signal Officer and Instructor Pilot for years in the EA-6B Prowler.  (acknowledged as more challenging to land than the Hornet) I can tell you with 100% certainty that is not the official technique that the Navy teaches.

I acknowledge that coordinated pitch and power inputs are required, my point is the Navy doesn't teach that pitch is the primary/first input for GS deviations.  Don't take it from me though, check out chapter 3.7 in the source for primary pilot CQ instruction:  https://www.cnatra.navy.mil/local/docs/pat-pubs/P-1211.pdf

@Micheal Hall obviously.  I am talking about the making of fine inputs to stay on slope.  You fly the airplane more or less the way the autopilot does.

No I think I said pitch and power input was used to correct glideslope deviation, not pitch alone then power.  It’s done and coordination.

Actually if you read that navy document,  you’ll notice they are in fact teaching pitch and power corrections for glideslope corrections.

Yes, you did say pitch and power for glideslope, but you said power only for airspeed, and claimed this was what the Navy taught.  That's what chafed me.  I also never said that it was absolutely always one to the exclusion of the other, and emphasized several times that both need to be used in a coordinated manner.  But, the basics I described were beat into our head from day one:  Power for glideslope, pitch for AOA.  At the ship if you are low and pull the nose up, or high and push the nose over, you will most likely get the happy lights and an opportunity to try again.

The proper way to intercept a glide slope is to use gentle pitch inputs that anticipate the changes in flight path from the power reduction you need to make to start descending without speeding up.  This is to short cut the airplane's natural tendency to hunt for its trim speed when power is reduced without making a pitch input.  Once on-slope and on-speed, the critical item is use of trim to get the airplane flying hands off at that speed on slope.  Then all that are required are gentle pitch/power inputs to hold the slope.
An ILS glide slope is a unique situation where you modify the normal pitch to speed technique because the priority is to stay precisely on a horizontal sloping path and making power changes and waiting for the airplane's static stability to take care of the speed is much too laggy.  And this is basically what autopilots do - they pitch to slope, and you just manage speed with power, with the autopilot taking care of trim, to the extent that the servos need to do so to reduce servo loads, in the background.
For hand flying a glide slope, the key is to know roughly what the power setting should be, and roughly what the pitch attitude should be while on slope and on speed.  As the needle comes down, you pitch over and make the power reduction at the same time so as the keep the airplane close to its trim speed through the transition.
Once on slope and on speed, you note the precise pitch attitude that exists, and concentrate on holding that attitude in your cross scan.  If you start to drift up, you pitch down one or two degrees and no more, make a small power reduction, and wait...  if not enough, make another degree or two of pitch/power adjustment and wait.  When back on slope and all is settled down, trim if/as required.  Proper use of trim is critical because you need to achieve a condition where the airplane naturally wants to hold the desired path/speed, and if you are out of trim and have to hold pressure yourself, you will inevitably relax without realizing it and drift off path.

When flying an ILS approach, you will be concentrating on using the attitude indicator to precisely maintain a pitch attitude.  In a typical GA plane, to make a small correction of the glide path, there's no need to touch the throttle.  Adjust the pitch attitude in the nose-up direction if you are low, and in the nose-down direction if you are high.  This method only works for airspeeds on the "front side" of the power curve.  For larger corrections you'll also want to make a power (throttle position) change to keep the airspeed near your target airspeed.
Other methods also work, but are more complicated and may make it harder to get the plane stabilized on the glide path.
This answer may be helpful in understanding the differences in dynamics on the front side versus the back side of the power curve:
Where is the 'zone of reversed commands...'?
Here is some more related content: Are we changing the angle of attack by changing the pitch of an aircraft?


text:
What is this WWII four-engine plane on skis?
I've seen this plane but I don't know its name:

Could you add a source for the image? A Google reverse image search finds World of Warships Arctic. Are you sure this is a real aircraft and not just from a game?

@Bianfable World of Warships Arctic makes a lot of sense, as that game focuses on the time period where this kind of machine could have seen action. Also, the bit of UI in the lower right gives it away :)

Yep, that's straight out of World of Warships. It's part of the pregame screen for a match on the Arctic map.

Note that the fantasy skis there are utterly impossible.  They would dig in to the snow!!  A wedge is precisely the opposite of a ski  :)  :)   Heh!

Well, I think.  I may be wrong, it may just be capturing the wrong angle.

Looks like a TB-3 or a variant thereof. According to Wikipedia, this four-engine all steel(!) heavy bomber first flew in 1930 and was the world's first cantilever aircraft in this class. The skis do not appear to have pertained exclusively to any specific variant, given that the first flight already used them.
It was used up to and including the Second World War, and a number of experimental variants were developed from it. One of the most interesting was the Zveno project, an experiment with parasite fighters. Here you can see the Zveno-SPB variant of the TB-3 with two I-16 fighters under the wings:

The Zveno-SPB saw operational usage and even success in raids against the Romanian oilfields during WW2.

Oh man, a bomber that drops fighters that drop bombs...

@Jpe61 6D chess :) The USAF also experimented with this concept later on, and came to similar conclusions.

@AEhere wonder why the USAF thought 6 inches of ground clearance was a problem :)

@Jpe61 Yo dawg, I herd you like bombers...

@jwenting indeed, I've seen less on modern-day hardware.

@AEhere the USAF can't assume it's airfields are perfectly smooth pavement.  They (and most other military operators) design around higher ground clearances so they can keep flying after just bulldozing most of the rubble back into the bomb craters and maybe dropping a steel plate on top to partially counter the roughness.

@DanNeely while my comment was mostly joking, the hardware I referenced was military in nature. Excessive optimism is not unknown in this area.

As yury10578 and AEhere correctly pointed out it's ANT-6A "Aviaarctica", polar version of TB-3 heavy bomber. (The plane's name is written on its body)
Its drawing in that exact livery:

ANT-6A with ski-only landing gear:

"Its drawing in that exact livery" Well, not exact. The OP's image has yellow accents. But quite close.

@T.J.Crowder Yeah, missed that. That's probably just some inconsistency of the drawings. Another drawing has something like those accents.

That must be one of the civil variants of TB-3 as other guys already said. Went under designations ANT-6A and/or G-2, I'd have to dig out a book to tell more precisely.
Interestingly, Wikipedia tells almost nothing about it -- and this plane (well, planes -- there were a small series) was quite a hero of Artic flights, if I recall my reading right.
ADDED: Well, it was (a hero etc.). On May 21, 1937 ANT-6A commanded by M.V.Vodopyanov (aircraft register number N-170) made ice landing in the North pole region, the first in history. Later, flight of 4 ANT-6A's landed the "North pole-1" polar expedition and their supplies.
The ANT-6A (actually, ANT-6 "Aviaarktika") modifications included a drag chute, which allowed to reduce a landing run by 35-50%. These aircraft could have either wheeled or ski landing gear. The cargo weight was up to 2500 kg, while the total load could reach almost 50% of takeoff weight.
G-2, however, and here I was wrong, was essentially TB-3 without the armament and with added cargo securing equipment and some "passenger carrying equipment"--hard seats (up to 4000 kg load or up to 50 passengers). Some of those registered thousands of flight hours.


text:
Why do pilots have to calculate their center of gravity? Couldn't this simply be measured?
I was watching Air Disasters, and one of the root causes of that episode's particular crash was due to the pilots underestimating their payload weight and being improperly trimmed for take-off.
This seems like an obvious and easily avoided danger.  Why don't they just include a sensor in the landing gear suspension system to measure the weight?  Adding up the weight each gear measures should precisely give you the total, triangulating them should tell you your center of gravity, no estimating necessary.
What's going on here?

Just out of curiosity, which episode/incident was that?

@sophit I didn't catch the beginning of the episode, I'm not sure.  It was a twin engine propeller plane though.  Sorry I can't be more specific.

@sophit I suspect it was Midwest 5481. Mayday / AIr Crash Investigation episode "Deadly Weight". (And before you ask, yes I do have a sadly photographic memory of most episodes of this series)

This series makes me wonder if the Smithsonian doesn't have enough imagination among its staff to come up with a better variety of subjects than constant repeats of Air Disasters.

A landing gear sensor system to calculate CG wouldn't work well on windy days.

Related - https://aviation.stackexchange.com/questions/44731/do-modern-aircraft-have-sensors-to-determine-weight-of-the-aircraft , https://aviation.stackexchange.com/questions/1850/do-some-airplanes-have-weighing-scales-on-the-landing-gear

Broadly, how might CoG be measured? How many of which typeof sensor might that need?

It would be possible to design a system that computes an airplane's weight and C of G from the landing gear load in real time, either by incorporating load cells into the gear legs, or measuring nitrogen pressure in each oleo (accuracy might be a problem there), and processing the data with an on-board computer. Or you could just include weight sensor pads on the tarmac somewhere, and weigh and compute the loaded airplanes as they taxi over them like trucks at a weigh station.
Problem is, you need to be able to forecast the all up weight and C of G beforehand anyway, to plan the load amounts and load distribution, fuel load etc. An on-board load sensing system only helps you after everything is complete.
Since you know the weight on the gears of the empty airplane before you started, it's just a simple math calculation to work out the numbers, and being able to do it beforehand allows you to adjust and tune your loading. It has a long history of being an accurate and reliable methodology, and incidents are too infrequent to justify major reform of it.
At the end, because a system to measure and compute the load on the gears in real time is kind of redundant, nobody is going to want to pay for such a system with the cost of certifying it.
So basically, there is no market or regulator demand for such a system. If a rash of incidents occurred that made it clear that the existing methods were unsafe, then you would probably see a move in that direction and start to see development of that sort of system.

"Problem is, you need to be able to forecast the all up weight and C of G beforehand anyway..." LOL! So true! "Folks, this is your captain, we're sorry, but one of you wasn't honest about your beer belly and now we have to return to the gate and rearrange everything."

Yeah imagine the chaos if the industry was forced off the "standard passenger weight" value used for loading the cattle car.

Also add the fact that the equipment will add to the empty weight of the aircraft, thus reducing its useful load.

This answer assumes that an adequately accurate load measuring system is merely a matter of cost, however that is not correct. As a result, a system like this could only ever by used as a fail-safe.

@JohnK Actually, Finland has started weighing pax at the gate on a "voluntary" basis. "Hello Mr... umm... Bubba? Would you mind stepping on the scale?"

It would be interesting to collect data on that and see if the pareto distribution of weights across the population upon which the standard weight is based matches reality.  Of course, I'm guessing the average Finn is somewhat lighter than the average North American.

It would be interesting to collect data on that and see if the pareto distribution of weights across the population upon which the standard weight is based matches reality.  Of course, I'm guessing the average Finn is somewhat lighter than the average North American.

On very small planes (<20 pax like Twin Otter or Cessna Caravan), it's pretty common to weigh every passenger anyway.

How does that work, please? Why is your load-sensing system not capable of providing readings every so often, if not in real time?

@MikeB That's not correct. I believe the Crane Airweighs system on the 777F was certified for operational use, the numbers that came from it can be used directly. It was shown to be within 1% of external aircraft weighing, which is a lot better than using standard passenger and baggage weights.

@MikeB Is that an STC? How does it work?

@JohnK If that was for me, it was Boeing factory option that apparently very few people ordered. Strain gauges on the landing gears. What I recall the marketing was in situations where you were close to being weight limited, finding you were a half ton lighter could prevent expensive delays and left cargo. Also, containerized cargo is easy to weigh and balance, but you also have charter carriers who are hired to ship a large industrial thing where the mass and CG aren't precisely known. You may have a reasonable upper bound on mass before you get there, but you still need to balance the plane.

Wouldn't it still be potentially useful to have the measurement of the CoG available after loading is complete? This would allow verification of the calculation. if the calculation was too wrong, then there is still an option to adjust.
Of course, this has to be weighed against the additional effort and the general severity of these errors.

@Chieron Personally, I think we should have this system (it's standard equipment for military transports) on new aircraft. As a cheap bit of extra safety. But it's hard to justify commercially if it can't replace the manual calculation.

Airbus Airplanes have load detection sensors in undercarriage legs, this allows autopilot to calculate CoG while still standing on Ground. Blessings +

Just for the record, in actual physics you can NOT calculate the true 3D cog of an object using such weight measurements against gravity on one surface. (A simple way to see this, the scales the wheels of the plane are sitting on, simply have utterly no idea of the height of the object (the plane) and hence no possible way of knowing at what point on Y the cog is.

@Fattie but the person who designed the plane knows the height of the object... So they could do a good job at approximating the value...

Hi @Questor. you misunderstand.  I added the "a simple way to see this" purely as a didactic aid to show how it is impossible to learn the THREE DIMENSIONAL cog (ie including the Y value) from the "scales under tires" method.  I can absolutely assure you that you can't get the exact Y value of the cog from the "scales under tires" method. (Sure you can guesstimate it.)

It's not only possible, it's been done on military transports and some cargo aircraft.
However, one still needs to know the aircraft's mass (not weight) prior to takeoff. Gear-mounted strain sensors get their data skewed by uneven surfaces, wind, and other factors.
Yes, installing such a system on all transport aircraft would have prevented a few accidents. It would not, however, free the crews of the need to calculate the aircraft's mass manually or via manual input. Strong wind near the ground can create lift and make an airplane appear lighter than it really is.
It's very useful for military planes, which might need to urgently transport cargo of unknown weight. Even with known cargo, wartime haste can greatly increase the risk of error. But for commercial cargo, weighing each container or pallet and calculating CG based on its location is much more accurate. Strain sensors could still be useful for double-checking, but they're not required and not often requested.

IIUC, if there's wind blowing on the nose of the aircraft, the wings will generate lift which will reduce the measured weight. Any wind blowing from the front 180° of the aircraft will reduce weight by some amount over each wing, possibly throwing the CoG calc off because one gear will report a lighter than actual weight while the other will report greater than actual. Do I understand correctly?

@FreeMan Yes. Wind anywhere over the wings will also shift the measured CoG. Not so much as to make it useless, but enough to make it a safety check only.

For airliners, the A300 had such a landing gear strain gauge system as an option, but nobody bought it. They tried again with the 777F.

But wouldn't weighing the pallets give you the weight, not the mass?

If I'm right about this being Midwest 5481 the incorrect calculation of Centre of Gravity was not the full cause of the accident.
Most, of not all, accidents are caused by a series of events - what is often refereed to as the swiss cheese model. In the case of this accident, it was a further aft CoG combined with improper maintenance. Had the pilots have had full elevator trim authority, they probably would have corrected the higher than expected pitch up caused by the aft CoG.
So, in answer to your question, the system doesn't exist because it's not needed.

Because it would be expensive and just add something else to the list of things to maintain. It's easier to calculate the empty weight CG and then add to that anything else you load on the a/c. Such gross mistakes in CG calculation are extremely rare, and the CG envelopes on airliners are relatively large, e.g. on the 777-200 the range is from 14% to 44% MAC (MAC=Mean Aerodynamic Chord, or the average distance from the leading edge to the trailing edge of the wing.)
A system that weighs everyone as they walk into the jetway would make more sense, but only for airlines. They are experimenting with this in Finland but they only ask for volunteers for now.

While this answer is a little less technical, it leads directly to the real answer: cost vs. benefit. The real cost of this system, including maintenance, training, etc., would greatly outweigh what already works. It points back to the (joking) question: if the black box on an airplane is indestructible in an accident, why don't they make the whole plane out of the same thing?

@StephanSamuel They did, it's just that all the parts want to abandon formation when they hit the ground.

From 2010 Boeing patent: "the present invention provides onboard aircraft weight and balance systems and methods for using them that are accurate, reliable, inexpensive, light in weight, and easier to calibrate, maintain and use in the field than prior art onboard weight and balance systems.". Note that sensing the forces on the wheels is not sufficient, the attitude of the aircraft must be known too (using the INS in this case).

@mins This assumes the aircraft is in still air, no wind, etc. That's probably the reason why it's not deployed on Boeing aircraft, to my knowledge. Is it?

Afaik, it's not deployed. It could be used as a safety net (perhaps precision is not required), but W&B calculation would still be required to not discover at the last minute there is a problem and the aircraft can't take off.

The short answer for cargo aircraft is because you always calculate the CG before you ever load the airplane.  You then load to achieve the calculated CG.  It's a proactive approach that's simple, accurate, fast, and cost effective.
If you load the airplane out of limits and catch it by measuring after the fact you would have wasted a bunch of time.
Not to mention all the drawbacks of such a system mentioned in other answers...

Just to complement the other answers a bit:
Sensors are normally already installed on the landing gears in order to indicate if weight is loaded on them and determine if the aircraft is on ground. These are termed Weight-on-Wheels (WoW) systems and are used to dis-/enable other systems: for example the thrust reversers are enabled on ground while weapons get disabled. Avionics also extensively uses these sensors.

Why don't they just include a sensor in the landing gear suspension system to measure the weight?

WoW systems are therefore already used and considered safety-critical.
There are several types of WoW sensors, ranging from the simplest mechanical switch mounted on the struct to magnetic proximity sensors based on the change of magnetic field associated with the damper's compression. Other systems (only proposed as far as I know) use strain gauges, cameras or even lasers detecting the landing gears extension. Those latter should be easy to be adapted and used to estimate weight and CG location.

When Concorde was being developed a knowledge and control of CofG prior to take off was important to maximizing fuel efficiency and range, as poor loading would require excessive trim and increase in drag.


text:
Why do pilots have control of so many functions that seem like they should be always-on?
I was watching this video about MH370, and I couldn't help but notice the pilot seemed to have options that could only ever be useful for nefarious purposes.
For instance, the pilot turned off the plane's transponder, he depressurized the cabin, and he powered the plane down so far that the ACARS satellite communications turned off.
Why are these things even possible?  Is there ever a good reason for any of them?  The only reason I can come up with is for maintenance purposes; but even then there's no reason the pilot should be able to do it rather than ground crew.

@Bianfable Partly, but it leaves the question about depressurization open.

If the pilot is that untrustworthy, pressurisation and transponders are the least of your worries.

Extremely simple case for just about any electrical system on the plane: What if that subsystem develops an electrical fault in flight? Should it take down the entire electrical system, or potentially start a fire, just because one thing broke? If it draws enough current it would trip the breaker (which is what allows the plot to turn it off), but what if it only draws enough to cause heating and excess current draw without enough to blow the breaker?

In contrast to driving your car, it is not possible to turn off the highway and go out to fix a problem when you are in a plane. Sometimes the way to continue to a safe landing is to turn off the disturbing system (it might be on fire). As modern planes does not have a mechanic the pilot has to be able to do everything from the cockpit.

They have control of them because they need to be turned off sometimes. For pressurization, a 737 has two PACKs (Pressurization and Air Conditioning Kits) which can be turned on or off independently. The pilot may need these under many circumstances:

To turn off the system on the ground when it shouldn't be running
If one PACK is inoperative
In certain emergencies like smoke in the cockpit or attempting an airborne restart of the engines

The pressurization system also has an outflow valve that can be used to change the pressurization or quickly depressurize the cabin. Quickly depressurizing the cabin could be required in flight to remove smoke or fumes from the cabin or on the ground in order to evacuate the airplane.

I'm neither a pilot nor an aerospace engineer, but just from my own sense of logic ...
If I was a pilot, I'd want control of as much as possible. With a little imagination I'm sure you could come up with a scenario where it would be a good thing to turn off or take some other action with any system. Any system could be malfunctioning and causing trouble. If an airplane is in trouble, they met well be over the ocean thousands of miles from the nearest land. The pilot wants to have the means to deal with anything that might happen.
Maybe it's true that 99% of the time there would be no reason to mess with X. But what about that other 1%? To say, "300 people were killed because there was nothing the pilot could do to correct the problem, because the engineers figured that, hey, MOST of the time there would be no reason for the pilot to mess with this", yeah, that would be a problem.
Not on the same scale, but ... Just yesterday I had a problem with a default setting in Microsoft Word. Fortunately for me I was able to change the setting, but I really had to search for it. Maybe it's true that 99% of the time, the default setting is fine and there's no reason to mess with it. But my case was the odd 1%.

Every switch doubles the amount of states in your system you have to consider, test and verify. It also increases the risk for failure. What if your switch to turn off critical thing X (which should be on all the time anyway) fails in an open state and now you don’t have X?

@Michael For a truly safe system, you'd have separate monitoring of critical thing X. That would cover the switch fault and any other fault in the cabling or system. And naturally you would have a procedure how to cope with the failure.

@jpa: All of that can quickly add a ton of complexity which can introduce new and exiting dangers and failure modes. Not to mention the impact on cost and performance and the human factor. Pilots, engineers and maintenance personnel would have to know about those redundancies and it can confuse them or distract them from the truly important things. There is no free lunch.

@Michael Well, you may think so, but that is generally the path that has been followed in safety-critical systems for decades now. Nobody builds systems where a critical component is not monitored, and as far as possible there are procedures for coping with failures (not necessarily through redundancy).

@micheal every subsystem already multiplies the possible states by N+1 where N is the number of failure modes. The switch attempts to cut that back to multiplying by two by unifying the behavior of the failure modes.

@michael Yes, if you add a switch to turn off X, you now introduce the possibility that that switch will fail. But many systems on airplanes are extremely complex. They already have hundreds or thousands of possible ways they could fail. If you could guarantee me 100% that the system will never malfunction, but that there is a high probability that a simple on/off switch will fail, sure, adding the switch increases the possible problems. But that's a very unlikely assumption. Adding the switch adds a minuscule amount of possible failure.

@jpa that works for trivial systems, but complex systems just provide too much information for a human to process easily. So the "every" is not done - even on purpose we skip it.

@Michael You have to test for those combination of states anyway because the system can fail by itself. The standard for "impossible" is very high: no greater than once per billion flight hours (115,000 flight-years). Almost nothing can reach this limit by itself.

Most of these switches are called circuit breakers.
The general idea is, if something shorts, it gets turned off one way or another. Anything that must be always on is a place to bring all avionics down because of a bus short through the device; and on a plane this big, loss of avionics leads directly to loss of control.
Yes I know most of avionics can be turned off, but there's a few things that actually are critical. If you can't command the hydraulic pumps because of a bus short your future flight time isn't very long.

Interesting to note that the "Airbus A380 has nearly 100,000 different types of electrical cables, with an estimated total length of about 300 miles… contribute to over 1,100 individual functions." https://simpleflying.com/airbus-a380-facts-figures-list/ Although wikipedia says wiring difficulties delayed production by 2 years and almost doubled development costs


text:
What did B-17 Pilots do?
Im making a game, and Im wondering what they did besides in combat, or bombing?
Futhermore, what did they do if they were in combat, and were heavily damaged?

They generally flew the planes.

In combat, heavily damaged, they Aviatated, navigated, communicated.
Back on the ground, they are, rested, recovered, planned for the next flight. If lucky, maybe some recreation. If not so lucky, mourne for some dead comrades.


text:
Can airflow reverse over the flight surfaces of a uav in high wind conditions
Can airflow reverse over the wing of a uav in high tail winds and low forward airspeed i.e 25knt fwd airspeed in a 35 knt tailwind? What would be the overall effect on the elevator and rudder? I suspect the rudder would be remain the same but operate at a reduced efficiency however, wouldn't the function of the elevator reverse and/or become ineffective, especially at high angles of attack? As a point of note, this uav does not have ailerons, I believe the roll effect is achieved as a combination of pitch and yaw.

No, at least, not in the way you seem to think.
When any aircraft flies, it does so relative to the air, not the ground. So, when you're watching from the ground, the air acts like a treadmill.
So, if you've got a 35kt South* wind, and a UAV that's flying North at 25kts, then, from the perspective of the ground, it will be traveling North at 60kts. It will still have 25kts of wind over its control surfaces, which will perform as normal.
If this UAV then turns around, it will appear from the ground to be flying backward, going North at 10kts even though it's facing south. But it will still have 25kts of wind across its control surfaces, which will perform as normal.
There are two ways to actually have a reverse airflow across its wings. You can reverse the thrust of the engine, or the wind can suddenly switch directions (as detailed in other answers). In either case, all control surfaces would function in reverse (assuming, of course, that whatever servo system moves the control surfaces is strong enough to fight the tailwind and actually move them).

*Remember, when discussing wind direction, you specify the direction that the wind is coming from. So a "South wind" would be blowing out of the South, toward the North.

If you're taking about a steady 35kt tailwind it would make no difference. The surfaces only react in relation to the air mass whether that air mass is moving or not.

It is possible, but only if there were a very sudden and dramatic change that the aircraft was unable to overcome.  However, it would be only temporary.
If the airflow direction was actually reversed the control surfaces would likely be blown to a full deflection position one way or the other depending on which side of neutral they were.
Otherwise, the aircraft would still move forward at 25kts relative to the moving airmass, with the additive effect of the wind giving it 60kts of ground speed.

You can test this with a simple balsa model and a desk fan.  Reversing airflow on both rudder and elevator will reverse the direction of their torquing force.  In the air, this has actually been seen with a model plane at around 15 mph hit with a strong gust from behind.  The elevator, pulled up to create downforce on the tail (to pitch the nose up), reversed, sharply pitching the nose down.  Needless to say, the wing lost lift as well.
A complete reversal in airflow in flight is extremely rare, requiring a huge gust.  Keep in mind the plane moves with the air mass in a constant wind.  But a gust need not drop your airspeed to negative numbers to cause a dangerous loss in altitude, as can happen in a microburst.  The remedy is to pitch down immediately and add power to regain airspeed.
Close to the ground, recovery may not always be possible.
But there is one practical application to your thoughts, positioning of ailerons while taxiing.
Is wind is quartering from behind, you want that aileron DOWN to help hold the wing tip down.  As you turn into the wind, having the aileron UP pushes the wing down (as in normal flight).  Same story with the elevator.  And a crossing wind can certainly prompt a rudder input.
Far more likely to experience these issues on the ground, and maybe not a good day to fly if they are happening in the air.


text:
What angle are front rotors of tandem helicopters tilted and why this value?
I've read that the front rotor of tandem helicopters are tilted forward so that you can get a forward velocity with no nose-down pitching of the fuselage, but what angle is used for this tilt and why this value?
Is this angular value chosen such that you can have no nose-down pitching at the design-point operation of the helicopter? ie, if the helicopter is designed to cruise at 150ktas, is the forward rotor's angle set such that your forward force cancels the total drag at this velocity and maintain no fuselage pitching? And if you wanted to go faster than 150ktas, you would just have to pitch the whole helicopter to get the rear rotor's upward thrust to join in to accelerate forward?

Somewhere a past question involved an answer with some interesting info on the Chinook helicopter.  It may or may not help answer your question.  I think the question was about how yaw control was achieved in this helicopter.

The forward tilt of the main rotors with respect to the fuselage is not related to the tandem rotor design, but to a combination of fuselage lift and the need to also provide thrust with the main rotor.
First off, a review of other tandem designs shows that those not related to the CH-47 do not always share the forward tilt:
Bell XHSL-1 prototype

Filper Research Beta 200A

McCulloch YH-30

Piasecki H-21B

Yak-24

And looking at non-tandem helicopters, we also find a similar tilt:
Sikorsky CH-53

NHIndustries NH90

Mil V-12

Mil Mi-26

The reason is twofold:
A helicopter obtains its thrust from the same place as most of its lift: from the main rotor. This means that in forward flight the main rotor will always have its tip plane slightly tilted forward to counter the drag acting on the airframe.
Furthermore, large helicopters like the tandem designs you ask about experience significant aerodynamic forces on the fuselage at high speeds. To mitigate these, the main rotors are installed at an angle so that in cruising attitude the lift component from the fuselage will be positive. You can see it more clearly in flight:
NHIndustries NH90 in flight

Sikorsky CH-53 in flight

Boeing CH-47D in flight

I could find some corroboration of the fuselage lift effect in this Boeing report which includes a lift curve for the fuselage attained via wind tunnel tests. As you can see $\alpha_{zero-lift} \approx 4.5^o$

As to what is the exact angle, that depends on the design and is ultimately optimized after extensive testing, if deemed worthwhile.

I never took into account the lift that could be attained by the fuselage. Thank you very much for this answer and for providing some new insight.